Hans Hahn (September 27, 1879 – July 24, 1934) was an Austrian mathematician who made contributions to functional analysis, topology, set theory, the calculus of variations, real analysis, and order theory.

Rudolf Carnap (May 18, 1891 – September 14, 1970) was an influential German-born philosopher who was active in Europe before 1935 and in the United States thereafter. He was a major member of the Vienna Circle and an advocate of logical positivism.

The son of a weaver, Feigl was born in Reichenberg (Liberec), Bohemia, and matriculated at the University of Vienna in 1922. He studied physics and philosophy under Moritz Schlick, the founder of the Vienna Circle, and received his doctorate in 1927 for the essay "Chance and Law: An Epistemological Analysis of the Roles of Probability and Induction in the Natural Sciences." He published his first book, Theory and Experience in Physics, in 1929. During this time,[1] became an active member in the Vienna Circle. He was one of the few Circle members (along with Schlick and Friedrich Waismann) to have extensive conversations with Ludwig Wittgenstein and Karl Popper.

Otto Neurath (Vienna, December 10, 1882 - Oxford, December 22, 1945) was an Austrian philosopher of science, sociologist, and political economist. Before he was to flee his native country in 1934, Neurath was one of the leading figures of the Vienna Circle.

Friedrich Albert Moritz Schlick About this sound listen (help·info) (April 14, 1882 – June 22, 1936) was a German philosopher, physicist and the founding father of logical positivism and the Vienna Circle.

Kraft studied philosophy, geography and history at the University of Vienna. He participated in the events of the University’s Philosophical Society, as well as with private circles (especially Oskar Ewald, Otto Weininger and Othmar Spann). He received in 1903 his Ph.D. with a dissertation on The Knowledge of the External World. Then he moved to Berlin to continue his studies under Georg Simmel, Wilhelm Dilthey and Carl Stumpf. Kraft started working at the University’s library in 1912. In 1914 he completed his habilitation under Adolf Stöhr with his book "Weltbegriff und Erkenntnisbegriff" (The Concept of world and the Concept of Knowledge). Kraft attend regularly the Vienna Circle until its dissolution, and at the same time was also a member of the Gomperz Circle and had contacts to the so-called periphery of the Vienna Circle (e.g., Karl Popper). Victor Kraft received the title of associate professor for theoretical philosophy in 1924.

Friedrich Ludwig Gottlob Frege (8 November 1848 – 26 July 1925, pronounced [???tlo?p ?fre??? ]) was a German mathematician, logician and philosopher. He is considered to be one of the founders of modern logic and made major contributions to the foundations of mathematics. He is generally considered to be the father of analytic philosophy, for his writings on the philosophy of language and mathematics. While he was mainly ignored by the intellectual world when he published his writings, Giuseppe Peano (1858–1932) and Bertrand Russell (1872–1970) introduced his work to later generations of logicians and philosophers.

Johann Nelböck, also Hans Nelböck (May 12, 1903, Brandel near Lichtenegg in Upper Austria–February 3, 1954, Vienna) was an Austrian former student of Moritz Schlick, who was the founder of the group of philosophers and scientists known as the Vienna Circle.

After attending the gymnasium in Wels Nelböck studied philosophy at the University of Vienna from 1925 on with Moritz Schlick, who was his doctoral advisor, and graduated as Dr.phil. on March 21, 1931, with the doctoral thesis "The Importance of Logic im Empirism and Positivsm".[1] Twice Nelböck was sent to an mental hospital with the diagnosis "schizoid personality disorder". He had threatened to kill Schlick.

Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS[1] (18 May 1872 – 2 February 1970) was a British philosopher, logician, mathematician, historian, and social critic.At various points in his life he considered himself a liberal, a socialist, and a pacifist, but he also admitted that he had never been any of these in any profound sense. He was born in Monmouthshire, into one of the most prominent aristocratic families in Britain.

Charles Sanders Peirce (play /?p?rs/ like "purse";[8] September 10, 1839 – April 19, 1914) was an American philosopher, logician, mathematician, and scientist, born at 3 Phillips Place in Cambridge, Massachusetts. Peirce was educated as a chemist and employed as a scientist for 30 years. Today he is appreciated largely for his contributions to logic, mathematics, philosophy, scientific methodology, and semiotics, and for his founding of pragmatism. In 1934, the philosopher Paul Weiss called Peirce "the most original and versatile of American philosophers and America's greatest logician".

Immanuel Kant (German pronunciation: [??ma?nu?e?l ?kant]; 22 April 1724 – 12 February 1804) was a German philosopher from Königsberg (today Kaliningrad of Russia), researching, lecturing and writing on philosophy and anthropology at the end of the 18th century Enlightenment.

At the time, there were major successes and advances in the sciences (for example, Isaac Newton, Carl Friedrich Gauss, and Robert Boyle) using reason and logic.

Ludwig Josef Johann Wittgenstein (26 April 1889 – 29 April 1951) was an Austrian-British philosopher who worked primarily in logic, the philosophy of mathematics, the philosophy of mind, and the philosophy of language. He was professor in philosophy at the University of Cambridge from 1939 until 1947. In his lifetime, he published just one book review, one article, a children's dictionary, and the 75-page Tractatus Logico-Philosophicus (1921).In 1999, his posthumously published Philosophical Investigations (1953) was ranked as the most important book of 20th-century philosophy, standing out as "...the one crossover masterpiece in twentieth-century philosophy, appealing across diverse specializations and philosophical orientations".Bertrand Russell described him as "the most perfect example I have ever known of genius as traditionally conceived, passionate, profound, intense, and dominating".